Pseudo-extension of frequency bands



April 12, 1938.

s. BAGNO 2,113,976

PSEUDO-EXTENSION OF FREQUENCY BANDS Filed Nov. 22, 1934 i I H o a: o z

'INVENTQR 4 then Patented Apr. 1938 PSEUDO-EX'IENSION OF FREQUENCY BANDSSamuel M0,: New York, N. 881811 by mesneassignmentatouuilLDeBola' AmmanNovember as, 1934, Serial No. maid v 6 Claims. (01. 119-1) Thisinvention deals with the gi elihodiand means of pseudo-extending thefidelity band of modulated circuits.

By pseudo-extensionis meant-the utilization 5 of a psychologicalphenomenon, such as that of the non-linearity of amplitude vs. responsecharacteristic of the ear, to increase the apparent frequency range of atransmitted signal; 'A fidelity band is that portion of the sensoryspectrum in which is necessary to faithfully reproduce the transmittedsignal to the brain.

- .One object of the invention is to provide a general method wherebyfaithful transmission and reproduction of .voice currents may be ac- 15complished with systems having a narrower fidelity hand than nownecessary.-

Another object of the invention is to provide a'method whereby thefidelity reproduction of radio receivers may be increased thru circuitmodification of broadcast transmitters.

Another object of the invention is to enable more faithful soundrecording and reproduction with amplifier systems having linearcharacteristics of limited range.

' Further objects and advantages will appear even tho wa 'm.

The explanation oflered for this phenomenon is that cross-modulation andan analogous Raman effect take place. If vm=nnn is the response todm, I

where Thus, it appears thatthe system exercises a dis the sameat'transmitter and receiver, the fidelity Let -now the responsive systembe a normal human ear, and mi a complex sound, such as music voice ornoise. Assuming a radiophone transmitter and receiver of linearcharacteristics and unit level adjustment, for the response to be handmust extend from'wi to 103. If however a network is introduced at thetransmitter such that while allowing free passage of 4m, (postulatingn1: =-'-i), 4123 is converted into 0mm, then 4m can be heard equallywell even tho the transmission band w3 u m may have been eliminated.

Hence also, a receiver with linear response over v be replaced asregards their effect on the sensory organ in question.

The general technique here presented is both novel and fundamental, andof wide application. 2 In various cases, even if 129 the introduction ofa modifying. network 0;: will often permit better results to be obtainedfrom say an amplifying system of useful range hi2 w au only.

Referring to the drawing, made schematic 3 since all elements used arewell known to those skilled in the communications art, 51: is a complexsound which is picked up and faithfully translated into electricalvariations by the microphone amplifier A. The frequencies w2 w wi 3 areblocked by the high-pass filter H. P., but permitted to pass freely tothe power amplification sections B via the low-pass filter L. P. Thefrequencies w3 w w2, while blocked by L. 9., are passed freely by H. P.into the rectifying network R where the (partial) conversion 0 m occurs.This component is thus also permitted to pass into B by L. P. From B,the currents are suitably transmitted as electromagnetic waves in thewellknown manner, or made to record thru suitable apparatus.

The block diagram in the upper left section of the figure is intended toshow a radio receiver or transmitter that may be coupled to the device(A-H. P.RL. P. and B) At the upper right. is shown a symbolic diagramfor a sound recorder or reproducing apparatus which may also beconnected to the device in 'such a manner as to utilize thecharacteristics of the invention to duced in the low frequency channelby a detector circuit, and the resulting components in this lowfrequency channel which fall into the range of the high frequencychannel are added to the high frequency channel and transmitted; asimilar effect may be obtained to pseudo extend the low frequencyspectrum. I therefore desire to have the illustrations included herewithand the descriptions specific thereto regarded in an illustrative ratherthan in a limiting sense. I do not desire therefore to be limited tospecific details of design, construction, or instrumentalitles employed,but having now set forth the object and nature of my invention, anddescribed means embodying the principle thereof, and illustrated themethod pertaining thereto. what I'claim as new and useful and of my owninvention and secure by- Letters Patent is:-- a

1. A method of distortion compensation in an audio circuit comprisingthe steps of: dividing the signal current'into high and low frequencybands, modifying the high frequencyband by detection, selecting'from thehigh frequency band the frequency components falling into the spectrumof the said low band, and adding said selected frequency components tothe said low frequency band and transmitting the bands so added.

2. A method of distortion compensation in an audio circuit comprisingthe steps" of dividing a signal current into high and low frequencybands, modifying the low frequency band by detection, selecting from thelow frequency band the frequency components falling into the spectrum ofthe said high frequency band, adding said se- 2 angers lected frequencycomponents to the said high frequency band, and transmitting the bandsso added.

8. In a distortion compensating network. an audio'input circuit designedand arranged to receive a predetermined frequency range. at least oneset of high-pass and low-pass sections. an

output section, wave distorting means associated output section, wavedistorting means associated with said low-pass sectionyland means fortransferring a component of the distorted current havingfrequenclesabove the upper cut-oi! of the low-pass section into the output section.and

means for transmitting variations. in current iii the output section.

5. In an audio frequency translation device,

7 means for collecting a band of frequencies, means for selecting fromsaid band substantially those frequencies which are preferentiallytransmitted and separating therefrom substantially the other collectedfrequencies at least, means for distorting the latter frequencies toones substantially within the first noted band, means for imposing thedistorted frequencies on said first band, and means for producing soundfrom the composite frequencies.

6. In an audio frequency translation device,

means for collecting a band of frequencies, means for selecting portionsof said band, means for distorting said selected portions, means forrecombining said selected and distorted portions with components of theoriginal band of frequencies;

means for selecting from the resulting composite frequencies, at least aportion thereof, and means for producing sound from said portion.

' SAMUEL BAGNO;

